As a solid electrolyte for battery, for example, PTL 1 discloses a silicon-containing lithium lanthanum titanate composite solid electrolyte material and a method of manufacturing the same. According to PTL 1, amorphous silicon (Si) or a Si compound is introduced to a grain boundary between lithium lanthanum titanate crystal particles by adding a lithium lanthanum titanate complex compound to a silicon precursor solution, heating and drying the mixture thereof, and then pelleting and firing the mixture. This indicates that the grain boundary ion conductivity is markedly improved.
In addition, for example, PTL 2 discloses a method of forming a titanium oxide type solid electrolyte by heating and firing a precursor solution containing water and a water-soluble titanium compound. According to PTL 2, since the precursor solution can contain each element supply source such as titanium, lithium (Li), and lanthanum (La) at a relatively high concentration, titanium oxide type solid electrolyte having a desired volume can be formed by reducing the number of times of applying and firing of a solution as compared with a sol-gel method using alcohol as a solvent.